WALTHAM – Three weeks from tonight, they will be scattering in different directions as the franchise’s longest offseason since 2007 begins.

With no playoff appearance for the first time since Rajon Rondo was a rookie in the 2006-07 season, the Celtics will have more than six months in between games.

Before the early vacation arrives, though, the Celtics have 12 games remaining, giving first-year coach Brad Stevens more time to evaluate what he has on the roster at the start of the rebuilding process.

At 23-47, the Celtics are moving along toward the finish line, trying to stay as focused as possible.

“It’s tough,’’ said Jared Sullinger before practice Tuesday, “but at the same time, we understand this is basketball and we get paid to compete.

“We’re competing every day, trying to get better every day. We understand the 12 games can carry over to next year.’’

In a scheduling quirk, the next four games are against two teams as the Celtics meet the Toronto Raptors tonight at the TD Garden (7:35, TV: Comcast SportsNet; radio: WBZ-98.5 FM) and travel to Canada on Friday night before hosting the Chicago Bulls on Sunday night and heading to the Windy City on Monday.

Stevens has kept a close eye on his players from training camp through late March and he is already making plans for the off-season schedule.

“It’s really important,’’ said Stevens of the months between the end of the season and the start of training camp. “The end of the season will be very structured as far as our meetings and what we’re going to do and as far as giving guys an idea of what the expectations are moving forward and what will help them grow their games individually.

“Each of these guys has a lot riding on that. I have no doubt they’ll work hard on it in the offseason and we’ll make ourselves available whenever they want us to be.’’

Rajon Rondo, whose season did not start until Jan. 17 due to knee surgery last year, plans to take two weeks off following the last game April 16 before diving back into workouts.

“I’ll probably ramp it up a little more (this summer), given the fact I’ll probably have a long break,’’ said Rondo, who’ll miss the playoffs for the second time in his eight years. “I’ll probably take a couple of weeks off from everything and let my body heal and go back to it earlier than normal. We’re usually playing till June or late May.’’

Stevens has gotten a good handle on his players and knows what areas they are going to have to work on this summer.

“The most tangible way for everybody to evaluate it is by their statistics in the game, but we get to see them every day,’’ said Stevens. “We get to see their work in the weight room, we get to see their work on the court, the practice habits, the shooting before (practice), their shooting after. All of those things add up.

“It goes back to when you’re on the floor, how efficient are you, and I think that’s something we all need to get better with. There’s no question about it.

“We’re not a very efficient team, especially on the offensive end of the floor. Hopefully we can continue to get better at that, and continue to grow in that.’’

Stevens, who spent his coaching career at Butler before taking over the Celtics last summer, will play more than double the amount of games he did in college by the time the season ends.

“There’s no much difference from a timing standpoint,’’ he said. “It’s just all condensed. One of the great learning things that I take from this year, and there are many things, would be what you need to do between the games.

“To be able to now have at least have a pulse on the (rest of the) teams and to know what they’re trying to do within their current systems is really good. As we get towards the end of the season, there’s a lot more familiarity. Now I’ve got a pretty good feel so I can focus more on us.’’

Jim Fenton may be reached at jfenton@enterprisenews.com. Follow him on Twitter at @JFenton_ent.